So, I haven't had my 99 C5 for long, but I bought it knowing it had some shifting difficulties. Over the past few weeks I had torn the rear end apart to get to the clutch and clutch master / slave. I ended up not replacing the clutch for various reasons, but the one that I took out and put back in I really don't think is the problem. The master and slave got replaced and properly bled. I was really hoping this ultimately was just a bad bleed job, but I was replacing cylinders and installing a remote bleed line just to be sure.

However, after reassembling everything with the new master / slave. The shifting problems continue. So, I figure it's only 2 possible problems left, the synchros, or the shift forks. I wanted to see what other people though. The problem is sometimes (more often than not) it is really hard to shift into first or second gear, as well as 5th and 6th. It feels like it shifts into place, but then if you let off the clutch you just get a lot of grinding. If holding pressure against the shifter while slowly letting off the clutch, it will sometimes clunk into place. Double clutching also seems to help.

I was going to swap the transmission as well while I had everything apart (found one that has 44k miles on it for a good deal, cheaper than having mine rebuilt, and for reference mine has 160k miles :p), but ran into delays with that being available and had to get the car back together for now. So, I do also have 4 quarts of gear oil, and I'm debating if I should drain the fluid in the current transmission and put that in there, or if it would just be a waste of fluid. I still might get the other transmission, just not sure when, nor if I'm ready to do this job again any time soon lol. While dropping the rear wasn't really hard, it is tedious, and not something I can do alone, so relying on others to have time to help means the car may be down for too long and I've got to try to find a time that I'm ok with it being down for multiple weeks (I generally can only get help on the weekends when I'm able to get it). And taking it to a shop is an iffy option, I don't really trust shops to do stuff right, haven't been able to find one that is just constantly in a rush to get the job done and careless since it's not their personal cars. Not to mention just because this job is so tedious, it's way more expensive than what I want to pay someone else to do it lol. But I do understand the cost, it takes a lot more hours of labor than a general transmission swap, just more than I want to pay right now.

But, like I said, I wanted to see what others thought. Does this sound like synchros for sure? Or is there a chance that changing out the gear oil would help? If there is not really any chance changing the gear oil will help I won't waste it and will just wait until I either get the transmission rebuilt or swap another transmission in.

Thanks

 

For starters, I'm assuming you've gone through the shifter alignment rigmarole and found no improvement to your issue. And based on your description, I don't think changing out the fluid will provide any major benefit... save that fluid for the next transmission (whether its a rebuild or different unit).

Usually there aren't really shift fork issues with these transmissions except for 3/4 because they used an aluminum 3/4 shift fork - but that can be upgraded to iron/steel. Shift rails aren't likely to be an issue either, assuming you can get into each of the shift gates without issue. So that kind of leaves component(s) within the synchro assemblies as the culprit... From my own experience getting grinding in 1st and reverse that was somewhat similar to yours, it's likely something to do with synchros. You won't know for sure until cracking into the trans, of course.

 

Not sure what year it was, but at some point they came stock with iron 3-4 forks and the 2 Corvette boxes I've taken apart also had billet 1-2 keys. OP you're going down the same path I did. First I did a new GM master/slave with remote adjuster and nothing else. Zero change. Next was an aftermarket non-self adjusting clutch. Made matters worse because it was stiffer and the weak hydraulics we're even more outgunned. Put in a Tick master, done. YMMV. There's a lot of these threads going around, maybe I should open a business. . .

There's also a drill mod for the master and slave. 1 orifice for the master, 2 for the slave but supposedly you can only reach the one because of the factory bend in the line.

 

Actually, no I haven't done any shifter alignment stuff. First I've heard about it. I'll look into it and give it a try as that is definitely easier than dropping the rear again, but not really holding out to much hope that it would make a difference. I actually have a new shifter to install anyway, got a MGW to put in but was thinking I'd wait and put it in when I had the shifting problem resolved to make sure I wasn't creating new problems lol. Also, the fact that double clutching seems to help is what I think really tells the tale of synchro issues I also feel like if it was an alignment issue, the shifter wouldn't click into gear sometimes while keeping force on it and lifting on the clutch pedal.

 

So, I went ahead and installed the MGW shifter, it came with a neutral alignment tool, so I figured that was the easiest way to make sure the shifter was aligned properly lol. While it does shift smoother, and easier to tell if it goes into gear or not, definitely does not fix the problem. So, I guess it's synchros. Sad day, have to tear all that stuff down again. And also fully remove this shifter to do it cause the shift box is bigger and barely even got it to fit, taking it back out is going to be a pain too =p

On the note of the MGW shifter though, it does have a nice short throw and feels nice and smooth... but damn it's heavy to go over to 1/2 or 5/6. Not sure I like that aspect of it.

 

I've got a '99 and, on arrival, it exhibited similar symptoms; first and second were very difficult to engage reliably, occasionally some others. It was a real hit-and-miss affair. I knew the car had been neglected, though, so I went through similar loops – fresh fluid for the clutch hydraulics, bleeding it as best as is possible in the original configuration, etc. I also changed the unknown but obviously ancient transmission fluid for fresh Amsoil Torque-Drive. The net result was that the grinding went practically immediately, as did the vast majority of the engagement issues.

Obviously, I can't attribute the result to one or the other – it was probably a combination, but probably most likely primarily related to clutch hydraulics – but, in any case, I'd certainly try a comparatively inexpensive fluid change first. It's easy, too. I had similar success in my old Subaru Forester with just a fluid change; a blend of new high-end fluids cured its reluctance to engage first at slow speeds and when cold, and greatly improved the action of the gearbox point blank (and it stayed that way for 12,000 miles, until I sold it).

The only step I need to take now in my C5 is to remove the original shifter tower (its bushings are a bit tired) and the aftermarket Hurst shifter, for similar reasons that you describe. The horizontal effort's a bit excessive and, in my shifter, its centering is a bit odd, all of which exacerbates any shifting-related issues. I've got a new C6 Z06 tower and shifter to go back in, which should hopefully serve up a decent middle ground.

 

TBH, I somewhat enjoyed rebuilding the T56 in mine despite all the hassle I went through for it. I'd even consider doing it again for someone local, lol.

Yeah, I bought a MGW at one point and wound up selling it with this being one of the main reasons. Heavy left/right motion on the shifter sucks for daily driving, and unfortunately the anti-venom mod only affects fore/aft motion. I went back to C6 + TMOD lower box, and recently shortened my C6 shifter for a little extra improvement.

 

I put an MGW in my race car and I love it. It helped me stop missing 3rd gear on an upshift (though missed 2nd on a few downshifts getting used to it). I would not want to DD it though, definitely requires you to be deliberate and committed.

 

Driving the car around some more today, there is something else I noticed it doing. This seems to happen only after I get everything nice and hot from driving around for a bit. But if after driving for a while I stop, and put the car in reverse, it will grind a little and the car will pull in reverse slightly even with the clutch fully depressed. It's not a continuous pull as if it's in gear, it's just a jerk initially. If I shift back into neutral and then back into reverse immediately it's fine. But if I shift into neutral and wait a few seconds, or shift into first and then back into reverse it does the same thing again.

Seems really odd to me that this happens with the clutch pedal fully depressed.

 

Here's an idea:
When the clutch pedal is out, the clutch, propeller shaft, and transmission input shaft are all spinning at engine speed and therefore have momentum. When you depress the clutch pedal, [assuming the clutch fully releases] all of the previously-mentioned components will begin slowing down, though I have no idea how long it takes for them to stop spinning.

One of the jobs of a synchronizer is to use its friction material to make the transmission input shaft match the output shaft based on which gear the trans is in. When entering reverse with zero wheel speed, the reverse synchro will brake the trans input shaft as reverse gear engages. So, perhaps when you're entering reverse the transmission input shaft is still spinning a little and the brief jerk you feel is simply the input shaft having speed and then decelerating from reverse engagement. Could be that the reverse synchro ring no longer can impart enough friction to adequately brake the input shaft... it's just brass after all and could be worn; all the other gears use a proper friction material on their synchros. (fun fact, you can replace the brass reverse synchro ring with one from 5/6 gear)

There's also the possibility that the clutch isn't 100% disengaging, which could allow the trans input shaft to have extra speed during reverse gear (or any gear) engagement. This is kinda what it sounds like, assuming the clutch pedal is depressed the whole time for when you mention going back into neutral and reverse. In neutral there's nothing in the trans preventing the input shaft from spinning up again.

You can minimize this behavior in reverse by first going into a different gear (which uses that gear's synchro to brake the trans input shaft), and then go into reverse.